CAROTENOIDS 



contains both chlorophyll and carotenoids, and Sapozhinkov ^ ^ * 

 claims that during photosynthetic reduction in the purple sulphur- 

 containing bacteria, carotene is converted into " xanthophyll " (but 

 see p. 121). Phototactic responses may, however, be mediated through 

 carotenoids in R. rubrum, according to a suggestion of French.* ^^^ 

 Recent work by Manten ^ ^ ' and Thomas ^ ^ ® has shown that this 

 suggestion is to a certain extent true, although Manten states that 

 bacteriochlorophyll plays an important part in this response. Thomas 

 has also found that the wavelengths of maximal efficiency for photo- 

 synthesis are the same as those for maximal phototaxis, viz. 590, 525, 

 490, and 460 mji, ; whether this by implication indicates that caro- 

 tenoids do play a part in bacterial photosynthesis remains obscure. 



Carotenoids may protect Sarcina lutea and S. amantiaca against the 

 adverse eflPects of ultra violet rays. ^ ^ ^^ 



Exogenous carotene may be important both as a growth inhibitor 

 and a growth promoter according to contradictory claims put forward 

 by Darzins^o^ and Vasileva^^* respectively. The former found that 

 [3-carotene inhibits the in vitro growth of the paratubercle bacillus and 

 the latter claimed that it stimulated the growth of abdominal typhus 

 bacteria. Darzins also noted an increase in the acid fastness of the 

 tubercle baculli grown on carotene containing media. This was due 

 to the elevation of the melting points of their constituent fats. Lutz ^ ^ ^a 

 has also considered the carotenoid content of Mycobact. Phlei strains 

 in relation to their acid-fastness. 



Luteraan, Champean and Choay ^ ^ o have speculated on the possible 

 role of carotenoids in the respiration of micro-organisms and recent 

 American work has shown that carotenoids can replace sodium acetate 

 in the nutrition of lactic acid bacteria. ^ ^ i 



Haas, Yenzi and Bushnell ^ ^ ^ claim that the failure to deplete human 

 subjects of vitamin A was due to intestinal synthesis of carotenoids. 

 In a comprehensive investigation with which the author was con- 

 cerned 1 1 ' this claim could not be substantiated ; bacterial cultures 

 from faeces of humans on a vitamin A deficient diet produced small 

 amounts of a very unstable pigment soluble in light petroleum but 

 which was not ^-carotene. 



ALGAE 



The carotenoids of the algae are not only interesting in themselves, 

 but also because of the role they play as precursors of vitamin A 

 in marine animals. Large numbers of workers have been interested 



* This has recently been demonstrated.*"' 

 128 



